Geologic dating techniques
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.All radiometric dating methods measure isotopes in some way.Most directly measure the amount of isotopes in rocks, using a mass spectrometer.These rates of decay are known, so if you can measure the proportion of parent and daughter isotopes in rocks now, you can calculate when the rocks were formed.Because of their unique decay rates, different elements are used for dating different age ranges.Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things.Stratigraphy is based on the law of superposition--like a layer cake, the lowest layers must have been formed first.
Like tail fins on a Cadillac, artifact styles and characteristics change over time, coming into fashion, then fading in popularity. The standard graphical result of seriation is a series of "battleship curves," which are horizontal bars representing percentages plotted on a vertical axis.
For example, fission track dating measures the microscopic marks left in crystals by subatomic particles from decaying isotopes.